1. Technical Field
This invention relates to a method for bending a tube and more particularly to a method for eliminating distortion at the end of a tube bend.
2. Background Art
Tube bending is well known in the art. Typically, machines for tube bending include a bending head having a bend die, a pressure die, a clamp die and a wiper die. Many machines also include a carriage which positions a tube with respect to the bending head and a numerical control which controls the various parts of the machine to bend a tube to a particular desired configuration. The known operation of the bending head is described more fully with reference to FIG. 1 in the Description of the Preferred Embodiment.
In mandrel-type tube bending, a mandrel is placed within the tube with the mandrel head at the point of tangency of the tube with the bend die. The tube is drawn over the mandrel as the tube is bent (i.e. as the bend and clamp dies are rotated), and the mandrel head thus helps to maintain the proper cross-sectional configuration of the tube through the bend. This is particularly important in bending tubes having relatively thin walls. Flexible mandrels are also used, having multiple ball links mounted to the end of the mandrel head and which thus extend within the tube beyond the point of tangency, to still further ensure maintenance of the proper cross-sectional configuration.
However, even with mandrel-type tube benders, the tubes when bent generally have a deformation in the wall at the outer radius at the end of the bend. The deformation is unattractive and the distortion may weaken the tube. Still further, the deformation results in non-uniformity of the interior surface of the tube, thereby causing flow turbulence which not only decreases efficiency of flow through the tube but also creates an accumulation point for contaminants.
The present invention is directed toward overcoming one or more of the problems as set forth above.